Study Note on 60CrMnMo Steel Roll Cladding Repair and Heat Treatment Process

Literature Overview

This study, published in Metal Heat Treatment in 2009 by Zhao Hui, Xu Ling from Shenyang University of Technology, and Fu Chenggang from Benxi Steel Co., Ltd. Roll Repair Plant, addresses the practical challenges of cladding repair and heat treatment of 60CrMnMo steel rolls. This is a highly practical study that bridges academic metallurgy with industrial roll repair operations, addressing one of the most common maintenance challenges in the steel rolling industry.

Core Technical Points

60CrMnMo is a medium-carbon alloy steel widely used for cold and warm rolling mill rolls due to its excellent combination of hardness, toughness, and wear resistance. However, during rolling service, rolls experience severe abrasion, galling, and surface fatigue, necessitating periodic repair. The cladding repair approach involves rebuilding the damaged roll surface with a wear-resistant overlay material, followed by appropriate heat treatment to restore the mechanical properties of both the overlay and the affected substrate zone.

The critical technical challenges in this application are:

Maintaining dimensional accuracy of the cylindrical roll surface during multi-pass overlay
Achieving uniform hardness across the full roll length
Preventing cracking in the thick overlay buildup
Controlling the heat-affected zone (HAZ) to avoid softening of the roll core

Parameter	Specification	Rationale
Substrate material	60CrMnMo (0.58C, 1.0Mn, 1.0Cr, 0.2Mo)	Base roll steel
Overlay consumable	Cr-Mo-V hardfacing wire or electrode	Wear-resistant surface layer
Overlay thickness	5–15 mm total buildup	Compensate for rolling wear
Preheat temperature	250–350°C	Reduce thermal stress, prevent cracking
Interpass temperature	200–300°C	Control cooling rate, prevent HAZ softening
Post-weld heat treatment	Temper at 560–620°C for 2–4 hours	Restore core hardness, relieve residual stress

Cladding Process Details

The cladding repair of 60CrMnMo rolls typically employs one of the following processes:

Submerged Arc Welding (SAW): Preferred for thick buildups (5–15 mm) due to high deposition rate and low dilution. Typically uses 3–5 passes with a flux-covered hardfacing wire. The flux composition is critical for controlling the microstructure of the deposited metal.

Gas Metal Arc Welding (GMAW): Preferred for thinner buildups (2–5 mm) and for achieving better surface finish. Uses solid hardfacing wire with CO₂ or Ar-CO₂ shielding gas.

Electroslag Welding (ESW): Occasionally used for very thick buildups on large-diameter rolls, though less common due to equipment requirements.

The key process challenge is maintaining the cylindrical geometry during multi-pass deposition. This requires:

Consistent travel speed and wire feed rate
Proper roll rotation control (typically 1–3 RPM)
Regular diameter measurement and compensation
Final grinding to dimensional tolerance (typically ±0.05 mm over 1000 mm)

Microstructural Evolution and Heat Treatment

The as-deposited overlay microstructure of a Cr-Mo-V hardfacing alloy on 60CrMnMo typically consists of:

Tempered martensite matrix (self-tempered due to alloy partitioning)
Primary carbides: Cr₇C₃, Mo₂C, and VC
Retained austenite (typically 5–15% depending on composition)

The heat treatment of the cladded roll is critical for achieving the target mechanical properties. The tempering treatment serves multiple purposes:

Residual stress relief: Reduces welding residual stresses that can cause dimensional instability during rolling service
Core hardness restoration: The HAZ of 60CrMnMo experiences tempering during welding, reducing core hardness; re-tempering restores uniform properties
Microstructure stabilization: Converts metastable retained austenite to tempered martensite + carbides, improving dimensional stability
Carbide spheroidization: Converts brittle carbide networks to more evenly distributed spheroidized carbides

Condition	Core Hardness (HRC)	Overlay Hardness (HRC)	HAZ Hardness (HRC)
As-welded	38–42	50–58	30–35
After tempering (600°C)	42–46	48–55	40–44
Target specification	44–48	50–58	42–46

Defect Analysis and Countermeasures

Defect Type	Cause	Detection Method	Countermeasure
Surface cracking	Excessive cooling rate, high carbon equivalent	Visual/MT	Increase preheat, reduce heat input
Undercut	Excessive travel speed, improper torch angle	Visual/UT	Optimize process parameters
Inclusion	Contaminated consumable or flux	UT/MT	Quality control of consumables
Hardness variation	Uneven heat input, variable dilution	Hardness survey	Process parameter optimization
Diameter out of tolerance	Uneven deposition rate	CMM measurement	Regular diameter monitoring

Engineering Practice Integration

The practical implementation of roll cladding repair requires careful coordination between the welding operation and the subsequent heat treatment. Key considerations include:

The roll must be cooled slowly after welding (typically in an insulated container or furnace) to prevent thermal shock cracking
The tempering treatment should be performed as soon as possible after welding to minimize the time the roll spends in a high-stress condition
The final grinding operation must be performed after the tempering treatment to ensure dimensional accuracy
A hardness survey should be performed at multiple locations (axial and circumferential) to verify uniform properties

The economic benefit of cladding repair over roll replacement is substantial: a typical 60CrMnMo roll can be repaired 3–5 times before replacement is necessary, with each repair costing only 10–20% of the replacement cost.

Key Reflections and Study Insights

This research exemplifies the practical engineering approach to roll maintenance, where metallurgical theory must be balanced with economic and operational realities. The key insight is that the cladding repair is not merely a welding operation but a comprehensive process that includes preheating, multi-pass deposition, controlled cooling, and post-weld heat treatment — each step critical to the final performance.

The study also highlights an important consideration often overlooked: the interaction between the overlay and the substrate during subsequent service. The thermal cycling experienced during rolling service can cause differential expansion between the overlay and substrate, potentially leading to delamination at the overlay-substrate interface. This risk is minimized by ensuring proper metallurgical bond (no oxide films or unmelted particles at the interface) and by selecting overlay materials with thermal expansion coefficients close to those of the substrate.